Zircon

Zircon is a mineral from the mineral class of "silicates and germanates" with the chemical composition Zr[SiO4] and thus, from a chemical point of view, a zirconium silicate, which structurally belongs to the island silicates. Very typical are partly high contents of hafnium, uranium, thorium, yttrium, cerium and other rare earth elements (REE). Zircon forms a gapless solid solution series with its much rarer hafnium-dominant analogue, hafnone. Reidite is a high-pressure modification of zircon.

The mineral crystallizes in the tetragonal crystal system and develops mostly short prismatic crystals with square cross section and pyramidal crystal ends as well as crystals with dipyramidal habit. The mostly ingrown, only rarely grown crystals can reach up to 30 cm in size. Zircon is also found in radially radiating aggregates, irregular grains, massive as well as in the form of unrolled, strongly rounded crystals. In its pure form zircon is colourless and transparent. However, due to multiple light refraction caused by lattice defects or polycrystalline formation, it can also appear white, although colorless to white zircons are rarely found. Mostly the mineral takes on a grey, brown to reddish brown and more rarely also yellow, green or blue colour due to various foreign admixtures.

Specimens that show gem quality due to their size and purity are a popular substitute for diamonds due to their diamond-like luster. Zircon is not to be confused with synthetically produced zirconia (formula: ZrO2, zirconium(IV) oxide), which also serves as a gemstone and imitation diamond.

Etymology and history

The name zircon comes either from the Arabic zarqun for "cinnabar" or from the Persian زرگون zargun for "golden". Altered, these terms are found in the name jargon, with which bright zircons have been named.

The name hyacinth (hyacinth), used since ancient times, originally referred to a blue or purple mineral. It comes from the Greek word Υάκινθος hyakinthos for "young man" - in Greek mythology, Hyakinthos was a flower created from the blood of the young man of the same name. As early as 300 B.C., the mineral had been named lyncurion by Theophrastus of Eresos after the Greek word λυγκύριον lyncurion. A mineral probably identical to modern zircon was called chrysolithos by Pliny the Elder in his Natural History (Naturalis historia), written about 77 AD. Called Hyacinthus by Georgius Agricola in 1546 and Hyacinthe by Barthélemy Faujas de Saint-Fond in 1772.

Jean-Baptiste Romé de L'Isle was the first to depict the characteristic crystal form of the zircon with prism and pyramid and to distinguish between columnar-elongated and pseudorhombic-dodecahedral varieties. Martin Heinrich Klaproth pointed out that Romé was the first to think of the jargon de Ceylan "as a special kind of stone ...". The mineral was first named zircon (Silex Circonius) in 1783 by Abraham Gottlob Werner, whose student Christian August Siegfried Hoffmann included zircon in the "Handbuch der Mineralogie" (Handbook of Mineralogy) he wrote after Werner's lectures.

In 1789 Martin Heinrich Klaproth analysed yellow-green and reddish zircons from Ceylon (today Sri Lanka) and discovered in them "a hitherto unknown, independent, simple earth", to which he gave the name "zircon earth" (terra circonia). Klaproth found the same earth in a hyacinth from Ceylon, whereby zircon on the one hand and hyacinth on the other proved to be "two species or genera of a peculiar rock family"; the new earth could possibly also be called "hyacinth earth". It was not until René-Just Haüy that hyacinth and zircon were united into a single mineral with exact determination of the crystal forms. The chemical element zirconium was first isolated by the Swedish physician and chemist Jöns Jakob Berzelius.

A type locality (locality of the material of the first description) for the zircon is not known, therefore there are also no correspondingly defined mineral samples (type material).

Red zircon from an unnamed locality in Pakistan

Classification

Already in the outdated, but still common 8th edition of the mineral systematics according to Strunz the zircon belonged to the mineral class of the "silicates and germanates" and there to the division of the "island silicates (nesosilicates)", where it formed the "zircon group" with the system no. VIII/A.09 and the further members coffinite, hafnon, reidite, thorite and thorogummite as eponym.

The 9th edition of Strunz's mineral systematics, valid since 2001 and used by the International Mineralogical Association (IMA), also classifies zircon in the division of "isosilicates (nesosilicates)". However, this is further subdivided according to the possible presence of further anions and the coordination of the cations, so that the mineral is to be found according to its composition in the subdivision of the "island silicates without further anions with cations in octahedral [6] and usually larger coordination", where it forms together with Coffinite, Hafnon, Stetindite, Thorite and Thorogummit the "zircon group" with the system no. 9.AD.30.

The system of minerals according to Dana, which is mainly used in English-speaking countries, also classifies zircon in the class of "silicates and germanates" and there in the division of "insular silicate minerals". Here it is to be found as eponym of the "zircon group" with the system no. 51.05.02 and the further members hafnon, thorite, coffinite, thorogummite and stetindite within the subdivision of the "inselsilicates: SiO4-groups only with cations in >[6]-coordination".